As the number of wireless communication stations joining a wireless network increases, the possibility problems such as collision, data loss, etc. increase. A collision requires data to be retransmitted that significantly affects the throughput of the wireless communication network. In particular, if a higher quality of service (QoS) is necessary for audio/video (AV) data and other such data, it is very important to secure more available bandwidth by decrease the occurrences of retransmissions.
Moreover, because of increasing demand for transmitting high quality video data between various home stations, the demand for a technical standard for transmitting and receiving high-quality video, which requires a broad bandwidth, is increasing.
Millimeter wave (mmWave) communication uses carrier frequency having a physical wavelength on the order of millimeters (i.e., frequency ranging between 30 GHz and 300 GHz) for very high rate data transmission. In general, this frequency band is an unlicensed band and has been limitedly used by communication service providers, in radio astronomy, in vehicle collision prevention, etc.
In a mmWave communication system, a carrier frequency of 60 GHz typically may be used with a channel bandwidth is about 0.5-2.5 GHz. Therefore, the mmWave communication system has a carrier frequency and channel bandwidth considerably greater than those of the conventional IEEE 802.11 series standard, respectively.
A mmWave carrier frequency is able to provide a very high transmission data rate of several gigabits (Gbps). A mmWave transmitter and receiver may be implemented on a single chip including an antenna having a size of less than 1.5 mm. Moreover, because the attenuation in air of mmWave signals is very high, inter-station interference may be reduced.
On the other hand, the high attenuation of mmWave signals reduces the range over which these signals may be effectively used. Therefore, it is difficult to transmit a mmWave signal omni-directionally. Beamforming may be used to solve this problem. Beamforming results in the mmWave signal being received by a reduced number of stations that are within the beam.
In a general method for generating a beam link, a transmitter forms beams in random directions and a receiver then responds back on a usable beam. After the link has been established, the searching process is repeated to account for any changes in the link. This is called “Tracking”. For this tracking and search, channel time is used. As the number of beam links increases in a given network, the time dedicated to the beam search and the tracking increases. Therefore, a method of performing theses processes most simply and efficiently is necessary.
FIG. 1 is a diagram that depicts an example of a short-range network according to an embodiment of the present invention.
Referring to FIG. 1, a notebook computer A, a monitor B, a personal media player (PMP) C and an external hard disk drive E may be mutually connected by a wireless communication network. In this case, a beam link may be established between the notebook computer A and the monitor B, a beam link may be established between the notebook computer A and the PMP C, and/or a beam link may be established between the notebook computer A and the external hard disk drive E.
FIG. 2 is a diagram depicting an example of beam patterns radiated by the stations shown in FIG. 1, respectively.
Referring to FIG. 2, a plurality of stations A to F may simultaneously radiate beam patterns. In this case, because frequency bands allocated to the stations differ from each other, interference generally does not occur.
In a network using the above beam links, a related art wireless communication system adjusts the data rate using autorate fall back (AFB). In the AFB, various data rate levels are available. The data rate may be raised by one level if data is transmitted at least ten times without an error. The data rate is lowered by one level if an error occurs in at least three consecutive data transmissions.